In the proposed study, neuronal development of the hippocampus of rabbit will be studied from time of birth to time of maturity; techniques will be used which focus on a uniform cell population and its synapses. With technical advantages provided by the in vitro slice preparation, it will be possible to obtain intracellular data providing information about passive membrane characteristics, appearance and efficacy of synaptic potentials, and capabilities of this hippocampal neuronal population for facilitative changes. Developmental changes observed electrophysiologically will be correlated with anatomical changes seen using routine histological and electronmicroscopic examination of tissue from the same animals. Intracellular dye injection techniques will be employed in conjunction with intracellular recordings to identify cell types, arborization of their processes and location of their synapses. Iontophoretic techniques will be used to test cell sensitivities to putative transmitter substances. These techniques should make it possible to study a given synapse in a comprehensive manner.